A Silicified Carboniferous Lycopsid Forest in the Colorado Rocky Mountains, USA

Abstract

The 1930 discovery of Carboniferous lycopsid fossils in south central Colorado resulted in the naming of a new species of scale tree, Lepidodendron johnsonii (=Lepidophloios johnsonii (Arnold) DiMichele). Cellular structures of L. johnsonii axes and periderm are preserved in silica—an unusual mode of fossil preservation for Pennsylvanian lycopsid plant remains. The early reports on the Trout Creek lycopsid fossils focused on taxonomic and paleobotanical aspects. Our 2019 reinvestigation of the locality produced many new specimens and a wealth of new data from a variety of analytical methods. Optical microscopy, X-ray diffraction, scanning electron microscopy, energy dispersive electron spectroscopy, determination of specific gravity, and Loss on Ignition provide details of mineralization. Cell walls are preserved with very small fine quartz particles, and cell lumina are filled with microcrystalline quartz. Some cell exteriors are encrusted with euhedral quartz crystals. These multiple forms of quartz are evidence that petrifaction involved several episodes of silicification. The dark color of the fossil wood and siliceous matrix appears to be caused by traces of dispersed carbon, but 500 °C Loss on Ignition reveals that the fossil wood preserves only very small amounts of the original organic matter.